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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

CHAPTER IX
FATTY   SUBSTANCES

Fatty substances consist essentially of combinations of various acids
of the fatty series with glycerine, and are obtained from vegetable organisms
(especially seeds and fruits) and from various parts of animals. Those
liquid at the ordinary temperature are termed oils, and those solid, fats.

The methods of analysis of fatty substances comprise determinations
of certain physical and chemical properties, commonly known as constants,
although they are constant only within certain limits, and also various other
investigations. The first part of the present chapter (General Methods]
contains descriptions of the more important determinations and tests carried
out similarly on all fatty matters. The second part (Special Part] deals
particularly with the more important fatty substances, the oils, vegetable
fats, terrestrial animal fats and fats from fishes and other marine organisms
being taken in order. For each class, tables are given showing the more
important data relating to the characters of the fatty substances more
commonly sold.

Closely analogous to fatty substances are the waxes, which consist of
compounds of acids with higher alcohols rather than with glycerine , they
will be treated after the fats, their general methods of analysis being the
same.

The more important industrial products derived from fatty substances,
such as stearine, oleine, glycerine, soaps, candles, etc., will be dealt with
in the next chapter.

GENERAL METHODS
1. Preparation of the Sample and Preliminary Determination

Before analysis, a fatty substance must be freed from any coarse im-
purities or water it may contain. For this purpose, a portion of the sample
is left for some time in an oven at about 60, when it clarifies if liquid and
melts completely if solid. It is then filtered through one or more filter-
papers, care being taken that any water collected under the fat does not
fall on to the filter.

With some fats, especially industrial fats, the water, other extraneous
matters (mucilaginous substances, residues of vegetable or animal tissues,
mineral matter), and total fatty substances have to be determined. The
procedure is as follows :

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